Water filter for aquatic breeding with prior art aims to purify the water body in the aquarium, assure the water quality of the water body is pure and fit for the healthy growth of ornamental fishes. As for water circulation system of the aquarium with prior art, its polluted water is pumped into the said water filter, and is filtered by the filter cartridge inside of the filter, and then purified water reflows from the water outlet to the aquarium. As is generally known, the critical component of the water filter is the filter cartridge, which intercepts and hold on suspended solid particles in the water, and serves the main task of filtering and purifying the water body, So, the filter cartridge will be saturated after a period of use, resulting in a great weakening of the filtration and purification function. Therefore, the filter cartridge has definite duration of usage and definite load limit. To play the maximum efficacy of the said water filter, any filter cartridge must be replaced when saturated or after a period of use. Nevertheless, the water filter can't remind consumers to replace the filter cartridge in due time, there is often the problem of poor water quality, affecting the growth and survival of the ornamental fishes, or waste due to prematurely replacement of the filter cartridge.